Network stations that use IP protocol require both a physical address and an IP address to transmit packets. In situations where the station knows only the network host IP address, the Address Resolution Protocol (ARP) lets you use the network station to determine a network host physical address by binding a 32-bit IP address to a 48-bit MAC address.
A network station can use ARP across a single network only, and the network hardware must support physical broadcasts. If a network station wants to send a packet to a host but knows only the host IP address, the network station uses ARP to determine the host physical address.
ARP response is enabled by default.
•Enabling ARP on a port or a VLAN on page 157
•Enabling ARP proxy on page 158
•Configuring ARP loop detection on page 158
•Showing ARP information on page 159
•Configuring IP ARP static entries on page 161
•Clearing ARP entries on page 162
•Showing ARP table information on page 163
Enabling ARP on a port or a VLAN
Before you begin
You must log on to the VLAN, or GigabitEthernet Interface Configuration mode in ACLI.
About this task
Enable ARP on the device so that it answers local ARP requests.
You can enable or disable ARP responses on the device. You can also enable ARP proxy, which lets a router answer a local ARP request for a remote destination.
Procedure
Enable ARP on the device:
ip arp-response
Enabling ARP proxy
Before you begin
You must log on to Access the VLAN, or GigabitEthernet Interface Configuration mode in ACLI.
About this task
Configure an ARP proxy to allow the platform to answer a local ARP request for a remote destination. ARP proxy is disabled by default.
Procedure
Enable ARP proxy on the device:
ip arp-proxy enable
Use the no operator to disable ARP proxy: no ip arp-proxy [enable]
Configuring ARP loop detection
Before you begin
You must log on to the VLAN, or GigabitEthernet Interface Configuration mode in ACLI.
About this task
Loop detection works only after you enable loop-detect. To clear this option, you must disable the loop detection.
Procedure
Configure ARP loop detection:
loop-detect [action {port-down|vlan-block|mac-discard}] [arp-detect]
Use the no operator to disable ARP proxy: no loop detect
To configure this option to the default value, use the default operator with this command.
Variable definitions
Use the data in the following table to use the loop-detect command.
Table 39: Variable definitions
Variable Value
action Indicates the action that the device takes:
port-down|vlan-block|mac-discard.
Showing ARP information
Before you begin
You must log on to the Global Configuration mode or the VRF Router Configuration mode in ACLI.
About this task
Show ARP port information to display data about the specified port, all ports, or the VLAN.
Procedure
1. Display ARP information for a specified port or for all ports:
show ip arp interface [gigabitethernet {slot/port[-slot/port]
[,...]]
2. Display ARP information for a VLAN:
show ip arp interface vlan <1–4094>
Variable definitions
Use the data in the following table to use the show ip arp interface command.
Table 40: Variable definitions
Variable Value
1–4094 Specifies the VLAN ID.
A.B.C.D Specifies a network.
gigabitethernet Specifies the interface type.
Showing ARP information
Variable Value
-s <A.B.C.D> <A.B.C.D> Specifies a subnet. You must indicate the IP address followed by the subnet mask.
{slot/port[-slot/port][,...]}] Specifies a slot and port or range of ports.
static-mcastmac Shows static multicast media access control ARP information.
[vrf WORD<0–16>] Specifies a VRF name. The total number of ARPs listed in the summary line of the "show ip arp" display represents the total number of ARPs on the chassis including all VRFs (which includes the Mgmt Router VRF).
[vrfids WORD<0–255>] Specifies a range of VRFIDs. The total number of ARPs listed in the summary line of the "show ip arp" display represents the total number of ARPs on the chassis including all VRFs (which includes the Mgmt Router VRF).
Use the data in the following table to use the show ip arp interface command.
Table 41: Variable definitions
Variable Value
PORT_NUM Indicates the port number.
DOPROXY Indicates if ARP proxy responses are enabled or disabled on the specified interface.
DORESP Indicates if the sending of ARP responses is enabled or disabled on the specified interface.
Use the data in the following table to use the show ip arp interface vlan command.
Table 42: Variable definitions
Variable Value
VLAN_ID Indicates the VLAN ID.
DOPROXY Indicates if ARP proxy responses are enabled or disabled on the specified interface.
DORESP Indicates if the sending of ARP responses is enabled or disabled on the specified interface.
Configuring IP ARP static entries
Before you begin
You must log on to the Global Configuration mode or the VRF Router Configuration mode in ACLI.
About this task
Configure ARP static entries to modify the ARP parameters on the device. The only way to change a static ARP is to delete the static ARP entry and create a new entry with new information.
Procedure
Configure ARP static entries on the device:
ip arp
Variable definitions
Use the data in the following table to use the ip arp command.
Table 43: Variable definitions
Variable Value
multicast-mac-flooding [enable]
Determines whether ARP entries for multicast MAC addresses are associated with the VLAN or the port interface on which they were learned.
Use the no operator to delete a static entry from the ARP table: no ip arp multicast-mac-flooding [enable]
To configure this option to the default value, use the default operator with this command.
request-threshold <50-1000> Configures the maximum number of outstanding ARP requests that a device can generate. The range is 50–
1000. The default value is 500.
To configure this option to the default value, use the default operator with this command.
static-mcast Configures static multicast MAC entries.
timeout <1-32767> Configures the length of time in seconds an entry remains in the ARP table before timeout. The range is 1–32767.
Configuring IP ARP static entries
Variable Value
To configure this option to the default value, use the default operator with this command.
<A.B.C.D> Adds ARP entries.
Clearing ARP entries
Before you begin
You must log on to the Privileged EXEC mode in ACLI.
About this task
Use this procedure to clear dynamic ARP table entries associated with the interface or VLAN.
Procedure
Clear ARP entries:
clear ip arp interface <gigabitethernet|vlan> <1–4084|slot/
port[-slot/port][,...]>
Variable definitions
Use the data in the following table to use the clear ip arp interface command.
Table 44: Variable definitions
Variable Value
1–4084 Specifies the VLAN ID if you choose the
VLAN interface type gigabitethernet|vlan Specifies the interface type
slot/port[-slot/port][,...] Specifies the slot and port or range of slots and ports if you choose the fast Ethernet or Gigabit Ethernet interface type
Showing ARP table information
Before you begin
You must log on to the Privileged EXEC mode or the VRF Router Configuration mode in ACLI.
About this task
Show ARP information to view the configuration information in the ARP table.
Procedure
Display the ARP table:
show ip arp [<A.B.C.D>] [-s <A.B.C.D> <A.B.C.D>] [vrf WORD<0-16>] [vrfids WORD<0-255>]
Variable definitions
Use the data in the following table to use the show ip arp command.
Table 45: Variable definitions
Variable Value
<A.B.C.D> Specifies the network IP address for the table.
-s <A.B.C.D> <A.B.C.D> Specifies the subnet for the table.
vrf WORD<0-16> Specifies the name of the VRF. The total number of ARPs listed in the summary line of the "show ip arp" display represents the total number of ARPs on the chassis including all VRFs (which includes the Mgmt Router VRF).
vrfids WORD<0-255> Specifies the VRF ID in the range 0–255. The total number of ARPs listed in the summary line of the "show ip arp" display represents the total number of ARPs on the chassis including all VRFs (which includes the Mgmt Router VRF).
Use the data in the following table to use the output of the show ip arp command.
Showing ARP table information
Table 46: Variable definitions
Parameter Description
IP_ADDRESS Indicates the IP address where ARP is configured.
MAC_ADDRESS Indicates the MAC address where ARP is configured.
VLAN Indicates the VLAN address where ARP is configured.
PORT Indicates the port where ARP is configured.
TYPE Indicates the type of learning (dynamic or local) where ARP is configured.
TTL<10 secs> Indicates the time to live as tenths of a second where ARP is configured.